1. Field of the Invention
The present invention relates to an optical multiplexer/demultiplexer utilizing optical fibers used for optical communication.
2. Description of the Related Art
An optical multiplexer/demultiplexer utilizing an optical fiber multiplexes a plurality of light beams or demultiplexes light into a plurality of beams. An optical multiplexer/demultiplexer provided for multiplexing is used to multiplex a plurality of light beams, and the light obtained by multiplexing is transmitted to an optical fiber. Another optical multiplexer/demultiplexer provided for demultiplexing is used to demultiplex the light transmitted through the optical fiber, and the demultplexed beams are transmitted to respective separate optical fibers.
In general, an optical multiplexer/demultiplexer utilizing optical fibers comprises a plurality of optical fibers, an optical filter for transmitting and reflecting light, and a lens. Light which has exited an end face of one of the optical fibers is converged or collimated by the lens such that it will not be spread, and the light reaches the optical filter to be demultiplexed into transmitted light that is transmitted by the optical filter and reflected light that is reflected by the same. The transmitted light and the reflected light thus demultiplexed by the optical filter are converged by a lens to impinge upon end faces of other respective optical fibers. Signal light is thus demultiplexed. Beams of light are multiplexed when they propagate in the direction opposite to that described above.
For example, such an optical multiplexer/demultiplexer is used in a WDM (Wavelength Division Multiplexing) transmission system. According to WDM transmission techniques, since a plurality of optical signals having different wavelengths are transmitted on a multiplex basis over a single optical fiber, the transmission capacity can be increased by an amount corresponding to the number of the wavelengths multiplexed. In order to provide such a WDM transmission system, an optical device such as an optical multiplexer/demultiplexer is required.
However, in the case of the above-described optical multiplexer/demultiplexer, it has been necessary to adjust the optical system or to align the optical axes of the optical fibers in order to allow transmitted light and reflected light demultiplexed by the optical filter to impinge upon the respective optical fibers efficiently. Further, there is a need for a housing for supporting and securing components such as the optical fibers and the optical filter, which has resulted in a problem in that the optical multiplexer/demultiplexer becomes large-sized and in that the optical multiplexer/demultiplexer involves a great number of constituent components and a great number of assembling steps.
As a solution to the above-described problems, a method is known, in which a graded index lens is attached to an end face of an optical fiber and in which an optical fiber ferrule and an optical filter are integrated at an end face of the graded index lens to reduce the size of an optical multiplexer/demultiplexer and the number of steps for assembling the same (Patent Document 1).
Another method is known, in which two single-mode optical fibers including a graded index optical fiber (hereinafter referred to as a “GI fiber”) attached on the end thereof are provided on one side of an optical filter constituted by a dielectric multi-layer film and another single-mode optical fiber is provided on another side of the filter and in which an end face of each of the GI fibers is processed such that it is at an angle to the optical axis of the fiber (Patent Document 2)
Patent Document 1: JP-A-2003-139962 (paragraphs [0023] to [0034], FIG. 1)
Patent Document 2: JP-A-11-38262 (paragraphs [0013] to [0025], FIG. 1)